How to find two successive and same values in a Stream?

Question

How can I find two successive and same values in a Stream and return this "duplicate-value":

def succ: Stream[Int] => Int = str => ...

For instance Stream(1, 2, 4, 3, 5, 5, 2, 2) would result in 5.

How would one do that?

Answer 1

Zipping the stream with its tail is another way of doing this which seems to handle single element Streams. Empty streams are handled explicitly:

def succ: Stream[Int] => Int = {
  case Stream() => 0
  case str =>
    str.zip(str.tail).
    find { case (l, r) => l == r }.
    map { case (x, _) => x }.
    getOrElse(0)
}